/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root == nullptr||root == p||root == q)
            return root;
        TreeNode* a = lowestCommonAncestor(root->left,p,q);
        TreeNode* b = lowestCommonAncestor(root->right,p,q);
        if(a&&b)
            return root;
        else if(a != nullptr&&b == nullptr)
            return a;
        else
            return b;

    }
};
